1. Field of the invention
The present invention relates to a clearance adjusting decelerator and an electric power steering apparatus having the same, and more particularly to a clearance adjusting decelerator and an electric power steering apparatus having the same in which a gear housing constructing a decelerator of a conventional electric power steering apparatus is divided into three parts: a rotary housing having a worm wheel housing and a worm/motor housing; a first worm wheel housing cap; and a second worm wheel housing cap, and the decelerator is assembled having the concentricity between a worm wheel housing pivot center axis and a worm wheel center axis of a first and a second worm wheel housing cap, and then the rotary housing relatively rotates to the first worm wheel housing cap and the second worm wheel housing cap when a worm tooth is matched with a worm wheel tooth so as to control the distance between the worm tooth and the worm wheel tooth, so that clearance is controlled.
2. Description of the Related Art
FIG. 1 is a diagram illustrating a conventional electric power steering apparatus. As shown in FIG. 1, the electric power steering apparatus 100 includes a steering system 130 connected from a steering wheel 102 to both side wheels 126, and an auxiliary power mechanism 140 supplying the steering auxiliary power to the steering system 130.
The steering system 130 includes a steering shaft 106 in which one side of the steering shaft 106 is connected to the steering wheel 102 so as to rotate with the steering wheel 102 and the other side of the steering shaft 106 is connected to a pinion axis 108 via a pair of universal joints 104. Further, the pinion axis 108 is connected to a rack bar 112 by a rack-pinion mechanism 110 and both ends of the rack bar 112 is connected to the wheels 126 of a vehicle by a tie rod 122 and a knuckle arm 124.
The auxiliary power mechanism 140 includes a torque sensor 142 for sensing torque applied to the steering wheel 102 by a driver and outputting an electric signal proportional to the sensed torque, an electronic control unit 144 for generating a control signal based on the electric signal transferred from the torque sensor 142, a motor 146 for generating the auxiliary power based on the control signal transferred from the electronic control unit 144, and a decelerator 150 having a worm 152 and a worm wheel 156 in order to transfer the auxiliary power generated in the motor 146 to the steering shaft 106.
Therefore, in the electric power steering apparatus, the torque generated by the rotation of the steering wheel 102 is transferred to the rack bar 112 via the rack-pinion mechanism 110 and the auxiliary power generated in the motor 146 based on the generated torque is transferred to the rack bar 112.
That is, the torque generated by the rotation of the steering wheel 102 and the auxiliary power generated in the motor 146 is combined so that the rack bar 112 can be moved in the direction of the axis.
FIG. 2 is a cross-sectional view illustrating a decelerator of a conventional electric power steering apparatus. As shown in FIG. 2, the decelerator 150 has a structure in which a worm shaft 254 formed with the worm 152 is provided wherein a first ball bearing 257 and a second ball bearing 258 are installed in both ends of the worm shaft 254, respectively, so as to support the worm shaft 254, and the worm shaft 254 is connected to a rotary shaft 270 of the motor 146 so that the worm shaft 254 rotates by the driving of the motor 146.
Further, the worm wheel 156 is provided in one side of an outer diameter of the worm 152 to be engaged with the worm 152 formed on the worm shaft 254, and is mounted on the steering shaft 106 which transfers the rotational force of the steering wheel 102 operated by the driver so as to transfer the rotational force of the worm shaft 254 generated by the driving of the motor 146 to the steering shaft 106.
A gear housing 260 includes the worm 152, the worm wheel 156, the rotary shaft 270 or the like therein, and the motor 146 for providing the driving force to the rotary shaft 270 is mounted on one side of the gear housing 260.
In the decelerator 150 of the electric power steering apparatus having the above structure, the electronic control unit 144 mounted on a vehicle controls the driving of the motor 146 depending on a driving condition of the vehicle and the rotational force of the worm shaft 254 generated by the driving of the motor 146 is added to the rotational force of the steering wheel 102 operated by the driver so as to be transferred to the steering shaft 106 such that smooth and stable steering can be achieved.
In the conventional electric power steering apparatus, the process of adjusting the gap between a worm gear and a worm wheel gear constructing the decelerator is required for managing clearance and noise. That is, the decelerator is manufactured through a complicated process in which the center distance of the worm gear and the worm wheel gear is firstly measured, the center distance of the gear housing and the worm wheel gear is secondly measured, and then the gap between the worm gear and the worm wheel gear is matched, so that there have been problems that the manufacturing process is complicated and an excessive amount of stock occurs.